Rigid filter assembly

ABSTRACT

Filter assembly for filtering solids from molten aluminum metal comprises at least one open-ended rigid refractory filter tube having an interior passageway, a bottom plate acting to close one end of such tube, a top plate having an aperture communicating with the interior passageway of such filter tube, and means, such as a tie bolt, with a fastener device to maintain the top and bottom plate and the interposed filter tube or tubes in sealed relationship so that the molten metal will flow through the walls of the rigid refractory filter tube without leakage at the ends or joints, to efficiently remove solid contaminants from the metal. The plates and tie rod or the like are of metal resistant to attack by molten aluminum, advantageously of cast iron. The refractory material of the tubes contains refractory particles resistant to molten aluminum and a bonding agent containing not over 10 percent silica.

United States Patent 1 Nowak RIGID FILTER ASSEMBLY [75] Inventor: ThomasA. Nowak, Livermore, Calif.

[73] Assignee: Kaiser Aluminum & Chemical Corporation, Oakland, Calif.

[22] Filed: June 9, 1971 [21] Appl. No.: 151,369

[52] 11.8. C1 210/238, 210/323, 210/510 [51] Int. Cl B0111 29/20, C04b21/00 [58] Field of Search 106/63; 55/502, 503,

11] 3,747,765 [451 July 24, 1973 Primary Examiner-Samih N. Zal'uarnaAssistant Examiner-T. A. Granger Att0rney-Paul Cabrow et a1.

[5 7] ABSTRACT Filter assembly for filtering solids from molten aluminummetal comprises at least one open-ended rigid refractory filter tubehaving an interior passageway, a bottom plate acting to close one end ofsuch tube, a top plate having an aperture communicating with theinterior passageway of such filter tube, and means, such as a tie bolt,with a fastener device to maintain the top and bottom plate and theinterposed filter tube or tubes in sealed relationship so that themolten metal will flow through the walls of the rigid refractory filtertube without leakage at the ends or joints, to efficiently remove solidcontaminants from the metal. The plates and tie rod or the like are ofmetal resistant to attack by molten aluminum, advantageously of cast:iron. The refractory material of the tubes contains refractoryparticles resistant to molten aluminum and a bonding agent containingnot over 10 percent silica.

7 Claims, 12 Drawing Figures PATENIEB 3. 747. 765

SHEET 2 BF 4 FIG. 6

FIG. 7 I

28K 1 INVENTOR. 31 THOMAS A. NOWAK PATENT ATTORNEY PATENIEU QMBH 3. 747.765

sums 0F 4 FIGS INVENTOR. THOMAS A. NOWAK PATENT ATTORNEY Pmmwww 3.141.765

SHEET u or 4 FIG. I]

INVENTOR THOMAS A. NOWAK PATENT ATTORNEY 1 RIGID FILTER ASSEMBLYBACKGROUND OF THE INVENTION Molten aluminum in practice generallycontains entrained solids which are deleterious to the final cast metalproduct. These entrained solids usually derive from three sources. Someare particles of aluminum oxide which are drawn into the liquid streamfrom the floating oxide layer on the surface, and some entrainedparticles are fragments of furnace lining, transfer trough and otherportions of the molten aluminum h'andling equipment which are eroded andentrained in the flowing aluminum stream; and some particles areprecipitates of insoluble impurities such as intermetallic compounds,borides, carbides or precipitates of other aluminum compounds, such asaluminum chloride. When these inclusions appear in the final castproduct after the molten aluminum is solidified, they cause such finalproduct to be less ductile, have lower strength or to have poorfinishing characteristics. Accordingly, it is desirable to removeentrained solids from the molten aluminum stream before it is cast intoa solid body which may be used as such or subjected to formingoperations such as rolling, forging, extrusions, etc.

Filtering processes to remove entrained solids from liquids areaccomplished bypassing the solid-laden liquid through a porous filtermedium that will not pass the solids. Filtering molten metal in general,and molten aluminum in particular, creates special problems because theliquid is so aggressive that it is difficult to find a filter mediumcapable of withstanding it. To avoid problems of deteriorating filtermedia, molten aluminum can be filtered through a bed of aluminaparticles.

In general, two methods of filtering are used for removing entrainedsolids from molten aluminum alloys before casting. The most commonfilter medium is an open weave glass cloth screen placed in the metaltransfer trough, around the spout or even in the molten metal pool inthe top of the solidfying ingot. These cloth screens are able to removeonly the larger sizes of inclusions from the metal and are easilyruptured during use because the glass fibers become very weak at thetemperature of moltenaluminum. In another prior art procedure, moltenaluminum is filtered through a bed of loose alumina particles, forexample, of tabular alumina, but it often suffers from the drawbacksnormally associated with bed filters in that it passes too many solids,there is a strong tendency to channeling which prevents efficient use,and pore size of the filter is not easily controlled but rather readilychanges under conditions of use so that, even when originally of properdimension, it cannot be efficiently maintained.

in U.S. Pat. No. 3,524,548, there has been disclosed a rigid porousfilter for filtering molten aluminum refractory filter medium in firedshaped form but it has been found that such rigid media filter tubes orelements are rather fragile and subject to breakage when a twisting orbending stress is applied. In order to reduce the cost of operation withthis filter medium, therefore, it has been desired to develop a devicewhich will enable efficient us of the rigid media filter element withreduction of breakage thereof and, consequently, reduction in the costof operation for this material. Such a device has now been developed andhas the advantages of lower cost operation, reduction in breakage withvery extended life of the filter tubes, and other advantages which willbecome apparent from the description below.

SUMMARY OF THE INVENTION According to the present invention, there isprovided a demountable cartridge for filtering molten aluminum whichcomprises in combination a. top plate, a bottom plate, at least one andadvantageously a plurality of rigid filter tubes or elements disposedbetween such plates, and means for fastening the assembly together andfor maintaining the filter media and top and bottom plates in sealedrelation with each other. Suitable rigid filter elements are describedin McDonald et al., U.S. Pat. No. 3,524,548, which issued Aug. 18, 1970.As there described, the rigid filter medium is a fired, shaped articlewhich includes a granular refractory material compatible with moltenaluminum, such as alumina, fused alumina, high purity bauxite ordiaspore, boron nitride or other suitable refractory material which isknown to resist attack by molten aluminum. The granular material isbonded together with a vitreous material containing less than 10% silicaand particularly as containing from 15% to boron oxide, from 5% to 50%calcium and from 2% to 60% aluminum oxide and not more than 10% silica.From 4% to 20% of the bonding material is advantageously used in makingthe rigid filter media. This suitable bonding material is described inU.S. PatpNo. 2,997,402, issued Aug. 22, 1961, in the names of Howard A.McDonald and James E. Dore.

The rigid filter media made, as described in U.S. Pat. 3,524,548 areexcellent filter means for molten aluminum metal but are rather fragileand care must be taken in the handling and use of the filters orcartridges in order to avoid breaking or shattering, with consequentincrease in costs of operation.

The device of the present invention enables more efficient handling ofthe rigid media filter and cartridge and reduces breakage losssignificantly. The plates and tubes are quickly assembled, and this canbe done by labor of minimum skill or training. The device can be pickedup and is ready for placement because it is not necessary to wait formortar joints to set. The cartridge can be readily disassembled whennecessary or when the casting operation has been completed, by looseningthe means holding the plates, tubes and tie rod together, lifting offthe top plate and removing the used filter tubes.

A particular advantage of the filter cartridge of this invention is thatsuch a cartridge has been found to have several times the useableworking life of a comparable but all-ceramic cartridge. Furthermore,when breakage or exhaustion of the filter element occurs, the cast ironparts of the device of the present invention can be re-used withreplacement of several sets of the ceramic filter tubes. A mostimportant advantage of this invention is the ability to pick up theassembled cartridge with a simple hook by lifting on the tie rod or bar.Previous all-ceramic assemblies were picked up by complicatedthree-point tongs which were difficult to 'operate at high temperatures.The all-ceramic assemblies were usually picked up by the top plate andif the mortar joints failed, the entire cartridge was dropped anddestroyed.

Another advantage is the ability of the device of the present inventionto withstand faster preheat rates, thereby reducing operating times andcosts. Another advantage is that cartridge shapes other than those ofround horizontal cross section are easily assembled, thereby increasingthe cartridge capacity with a minimum increase in the space required.

BRIEF DESCRIPTION OF THE DRAWINGS The invention and some modes ofcarrying it out will be illustrated and described by the followingspecific description and by the annexed drawings in which:

FIG. 1 depicts one embodiment of the filter cartridge device of thisinvention in assembly, in a perspective view;

FIG. 2 is a cross-section of the assembly of FIG. 1, taken on line 2-2;

FIG. 3 is a perspective view toward the lower surface of the top plateof the assembly shown in FIG. 1;

FIG. 4 is a perspective view toward the top surface of the bottom plateof the device of FIG. 1;

FIG. 5 is a perspective view of one embodiment of a tie rod of theassembly of FIG. 1;

FIG. 6 is a vertical cross-sectional view of one embodiment of theassembly of this invention, showing it in place in a filtering zone orunit, and ready for use;

FIG. 7 is a vertical cross-sectional view showing another embodiment ofa tie rod according to this invention, showing the rod in position withrespect to a bottom plate of the assembly of this invention;

FIG. 8 shows a device for grasping, lifting and transporting a filtercartridge made according to the present invention;

FIG. 9 is a cross-sectional elevation view showing another embodiment ofeach of the plates and another fastening means;

FIG. 10 is a top plan view of the fastening device of FIG. 9, the restof the device being cut away for clarity;

FIG. 1 l is a perspective view of another embodiment of the cartridge ofthis invention, having a simple tube; and

FIG. 12 is a schematic top plan view of a further arrangement ofmultiple tubes and tie rods.

DETAILED DESCRIPTION OF THE INVENTION In the embodiment of a filterdevice shown in FIGS. 1-5, the demountable assembly 10 includes a topplate 11 having in it a plurality of holes or apertures 12 and a bottomplate 13, both plates being of cast iron. Disposed between the platesand sealed respectively to the lower surface 22 of plate 11 and theupper surface of plate 13 are a number of filter tubes 15 of the rigidfired refractory material hereinabove. That is to say, these tubesconsist essentially of a shaped, fired admixture of alumina particleshaving a maximum diameter of between 1.165 mm. and 2.8 mm., bonded withfrom 4% to of a prefused vitreous bonding material containing from 15%to80% boron oxide, from 5% to 50% calcium oxide and from 2% to 60%aluminum oxide, and not more than 10% silica. As shown in FIG. 2, plates11 and 13 and tubes 15 are held firmly together by a tie rod 16 of thetype shown in FIG. 5. Plates 11 and 13 are each provided with a centralaperture at 17 and 18 respectively. In this embodiment, the walls of 18are threaded and the lower end 19 of tie rod 16 is also threaded so thatit can be threadedly connected tightly to plate 13 within aperture 18,tie rod 16 being circular in horizontal cross-section. Tie rod 16 isalso provided with an annular shoulder 20 at its upper end, to fit intoannular recess 14 in the lower surface 22 of top plate 11; and a lowerannular shoulder 21 fits into recess 34 in upper surface 23 of lowerplate 13. At its top end, tie rod 16 is provided with an extension 24 ofreduced cross-section which extends through aperture 17 and upwardlyfrom top plate 11. In this embodiment, the plates and tie rod are madeof heat-resistant cast iron available in commerce under the trademarkAtlas Alloy 220, made and sold by Atlas Foundry, Tacoma, Wash.

Rigid filter tubes 15 are circular in horizontal crosssection in thisembodiment, although the crosssectional configuration is not criticaland other shapes can be selected if desired. However, the circularcrosssectional tubes are generally most suitable to make and use. Eachsuch tube 15 is provided with an internal passageway 25 whichcommunicates with an aperture 12 in upper plate 1 1, the walls ofpassageway 25 and of aperture 12 being in alignment or registration sothat a smooth flow of metal results. In this embodiment, an annularrecess 26 is provided in the wall of each aperture 12 to accommodate orreceive the upper end of tube 15 in such relationship. Interposedbetween the surface of plate 11 and the end of each tube 15 is acompressible, aluminum-compatible sealant material, which in thisinstance is a gasket 27 of Fiberfrax which is an alumina-silica fibroussheet material useful at temperatures above 2,000 F. and made and soldby The Carborundum Company. Disposed in upper surface 23 of plate 13 area number of circular recesses 28 which register with the apertures 12 inupper plate 11 and which receive the lower end of tubes 15. A sheet ordisc 29 of a like sealant material, such as Fiberfrax, is interposedalso between the surfaces of recesses 28 in plate 13 and the ends oftubes 15. A thicker layer 37' of Fiberfrax is also placed between thesurface of upper plate 11 and the upper end of rod 16, because as rod 16expands upon heating, this layer will compress accordingly andaccommodate for such expansion. The upper portion, or extension 24 ofrod 16 is at least partially threaded in this embodiment. In assemblyingthis device, tie rod 16 is threadedly connected to lower plate 13 andthe required number of tubes 15 are set in their respective recesses 28,after which top plate 11 is placed over the tops of the tubes and tierod 16, with suitable implacement of the Fiberfrax discs and gaskets,and the whole fastened together by suitable means. A sleeve 30 is placedover the upper extension 24 and a retaining nut 33 is screwed down overthe upper portion of extension 24 to tighten sleeve 30 and extension 24against plate 11 and to hold the entire assembly in secure attachment.Instead of the tightening nut 33, any other suitable quick-disconnectdevice can be used, e.g., a cam arrangement as will be described below.When the cartridge, is heated to the temperature of operation, the castiron tie rod that the sleeve and top plate must be tightened against thetops of the filter tubes. Conversely, upon cooling after a drop orcasting operation is finished, the fastening device is quickly loosenedto permit adjusting again the position of the sleeve and plate. A pairof arms 35 extend outwardly from retaining nut 33 and, as shown in FIG.8, assist in lifting and transporting the entire assembly. In FIG. 6 isshown the implacement of the device in the filtering zone or housing 40having an entry pipe 36 for introduction of hot molten metal from amelting zone or the like and an outlet 38 provided with a suitable cap(not shown), to assist in draining and cleaning the device. The filtercartridge or assembly made according to this invention is placed infiltering chamber 40 which includes lower or inlet portion 41 forintroduction of hot metal coming through inlet 36, and upper or outletchamber 42 which receives filtered metal from filter tubes and conductsit to outlet 44, whence it fiows to casting stations. Upon chamber 42 isprovided with a lid or cover 43 so that the hot filtered metal is keptout of contact with the air. If desired, and advantageously, an inertgas can be introduced into chamber 42 above the level of the metal byconventional means to assist in maintaining nonoxidizing conditions. Thetop plate 11 of filter cartridge 10 rests at its outer edge of anannular shoulder 45 provided at the upper end of lower portion 41.Bottom plate 12 is supported by tie rod 16 and is of smaller diameterthan top plate 11 and also of smaller diameter than the interior oflower portion 41 so that passageway for molten metal is providedaroundthe circumference of lower plate 12. Other means of conductingmolten metal into contact with filter tube 15, such as holes in plate 13could be used, alterna-f tively. The upper end 46 of tie rod 16 is atsuch distance from the upper surface of plate 11 that cover 43 rests onsurface'46 and thereby plate ll is held down in sealed connection withshoul dr 45 against the force of metal being filtered through tube 15when the device is in operation. Advantageously, compressible sealantgasket 47 is placed between shoulder 45 and the outer edge of plate 11to ensure that no leakage will occur. Instead of a lid or cover, a baracross the top of outlet chamber 42 can serve to hold down the rod andcartridge.

In FIG. 7 there is shown an alternative lower portion of a tie roduseful herein. In this arrangement, tie rod 48 is provided at its lowerend with a flange or discshaped end piece 49. Plate 13 is provided withthe central aperture 18 and with an annular recess 50 at the lower endthereof so that the disc-shaped end 49 of tie rod 48 fits snugly intorecess 50, the central stem of tie rod 48 extending upwardly throughaperture 18' in plate 13'.

In FIG. 8 there is shown one means of grasping, lifting and transportingthe filter cartridge of this invention, all but the top portion of thedevice being cut away for simplicity. In this embodiment, sleeve 30 isin place resting on plate 11 and held tightly against that plate bymeans of nut 33 which is screwed tightly against the top of sleeve 30.Extending arms 35 are provided on nut 33. A double-hooked grasping means52 is slipped over arms 35, and is provided with a top eye or graspingmeans 53 by which the device can be lifted,

either by hand or by suitable mechanical means. The

surface 60, no recesses being provided in either plate to receive thetube ends. In this embodiment, it is advantageous that each plate can bemade by casting without any machining so that all surfaces in contactwith molten aluminum are of cast metal, advantageously cast iron, asdescribed, and provide better resistance to attack by the aluminum.

The tie rod 62 in the device of FIG. 9 is a straight shaft havingflanged end 63, and at its upper portion extending upwardly throughaperture 64 in plate 55. A metal sleeve 65, also suitably of cast metal,e.g. cast iron, surrounds shaft 62 above plate 55 and a compressiblesealant gasket 66, such as described elsewhere herein, is disposedbetween sleeve 65 and plate 55 to seal against leakage of moltenaluminum between rod 62 and the wall of aperture 64. At the top ofsleeve 65 is disposed another such sealant gasket 67 and above that is awasher 68, suitably of steel. A pin 70 passes through shaft or rod 62and supports a pair of cams 71, 71' and a bifurcated arm 72 whichextends from each cam outwardly. Arm 72 can be quickly moved to adjustthe position of the cams as rod 62 expands on heating or contracts oncooling, pressing the faces of the cams against washer 68 and holdingthe sleeve 65 and gasket 66 in sealed relationship with plate 55. In onemanner of operation, a counter-weight can be suspended at the outer endof arm 72 to maintain cams 71, 71' in contact with the washer, sleeveand sealant combination to maintain the desired sealed re lationship.

In FIG. 11 there is shown a perspective view of another embodiment ofthe present invention wherein there is employed a single rigid tube 75and a top plate 76 having a single aperture 77 which registers with theinterior passageway of tube 75, and a bottom plate 78 which closes thelower end of tube 75. It will be under stood that suitable sealants (notshown) are disposed between the tube ends and the plates. A tie rod 79,extends upwardly from the bottom plate 78 through the tube 75 andaperture 77, and a plurality of arms 80 extend from a collar 81 disposedaround rod 79 to the outer edge 82 of plate 76 and clamp over edge 82.Arms 80 thus act to hold plates 76 and 78 and tube 75 together and tocenter rod 79 when this device is assembled and a fastening means (notshown) is applied to upper extension 84 of rod 79. i

In FIG. 12 there is shown schematically a top plan EXAMPLE A filtercartridge 10 was assembled as shown in FIGS. 1 through 5 and waspre-heated to 1,300 F. in an electric oven at the rate of 350 per hour.The assembly was re-tightened by screwing down the nut 33 to take up thethermal expansion of the tie rod 16 before the cartridge was removedfrom the pre-heater.

The pre-heated cartridge 10 was then lifted out of the pre-heater andplaced in the filter chamber 40 with the proper gaskets- Molten 7075aluminum alloy was filtered through the assembly at a temperature of1,300 F. and at a rate of 300 pounds per minute while casting two 49sheet ingots. After an ingot length of 114 inches had been reached themetal flow was stopped. The filter cartridge 10 was allowed to remain inthe filter chamber while the ingots were removed from the castingstation.

Casting was again started and molten 7075 aluminum alloy at 1,300 F. wasfiltered through the cartridge at the rate of 300 pounds per minute. Theprocess was repeated as described above until filter cartridge was nolonger usable or after approximately 100,000 pounds of molten aluminumhad been filtered. Filter pressure buildup was good, indicating noleakage for the cast, and no filter tubes broke in the handling. Thequanity of the metal cast was also good, with good removal of solidparticles of impurities.

It will be understood that the above specific description and drawingshave been given for purposes of illustration and explanation only, andthat variations and modifications can be made therein without departingfrom the spirit and scope of the appended claims. For instance, morethan one tie rod can be employed, e.g., a pair of such rods disposed indiametric opposition in the assembly. The cast iron of the metal partsused herein, including the walls and parts of the filter chamber andoutlet chamber, is advantageously heatresistant cast iron.

Having now described the invention:

I claim:

1. An assembly for filtering molten aluminum metal comprising a filterchamber and disposed therein in sealed relationship a filter cartridge,means to maintain said chamber and said cartridge in sealedrelationship, and outlet means for filtered metal, said cartridgecomprising,

a. a top plate of cast iron having a centrally disposed, tierod-receiving aperture, an upper surface, a lower surface, and an outeredge,

b. a bottom plate having an upper surface, a lower surface, an outeredge and a centrally disposed tie rodreceiving aperture aligned withsaid first-mentioned aperture,

c. a plurality of rigid filter tubes, each such tube having an interiorpassageway and consisting essentially of a shaped, fired admixture ofrefractory particles resistant to molten aluminum and having an averagemaximum diameter of from about 0.165 mm. to about 2.8 mm. and from 4% toby weight; based on total fired weight of the admixture, of a prefusedvitreous product consisting essentially of, by weight, from 15% to boronoxide, from 5% to 50% calcium oxide and from 2% to 60% aluminum oxideand not more than 10% silica,

d. said top plate having a plurality of secondary aper-, tures disposedbetween said outer edge and said central aperture, each such secondaperture communicating with the interior passageway of a rigid filtertube,

c. said bottom plate having a plurality of recesses disposed in saidupper surface between said outer edge and said central aperture, eachsuch recess being aligned with one said second-mentioned aperture andpassageway,

f. a compressible refractory sealant disposed between the end of eachsaid rigid filter tube and said upper and lower plates to effect sealedrelationship therewith, and

g. a cast iron tie rod extending between said upper and lower plate andthrough said central apertures to maintain said plates and tubes insealed relationship, and

h. means to detachably fasten said plates and said tie rod in firmassembly, and mans to maintain said chamber and said cartridge insealedrelationship.

2. An assembly as in claim 1, having also means to grasp and lift saidcartridge.

3. A demountable cartridge for filtering molten aluminum comprising incombination:

a. at least one filter tube having an interior passageway and formed ofa rigid porous material having inner-communicating pores, said materialconsisting essentially of a fired mixture of refractory particlesresistant to attack by molten aluminum, said particles having an averagemaximum diameter of from about 0.165 to about 2.8 mm, and a prefusedvitreous bonding material consisting essentially of, by weight, from 15%to 80% boron oxide, from 5% to 50% calcium oxide and from 2% to 60%aluminum oxide and not more than 10% silica said bonding material beinguniformly dispersed throughout said mixture, surrounding said particlesand adhering them together,

b. a first metal plate resistant to attack by molten aluminum adjacentone end of said filtering tube, said plate having at least one apertureadapted to receive a tie rod and an aperture for each filter tubeadapted to be in fluid communication with the interior passageway ofsaid filter tube and having a peripheral recess in the under face of themetal plate,

0. a second metal plate resistant to attack by molten aluminum adjacentthe opposite end of said filter tube, said plate having in its upperface a recess for each filter tube and means for attachment thereto ofsaid tie rod,

d. a compressible refractory sealant material resistant to attack bymolten aluminum disposed between the ends of each filter tube and saidplates, whereby the plates and tubes are maintained in sealedrelationship upon expansion thereof, and

e. at least one tie rod and fastening means formed of a metal resistantto attack by molten aluminum joining said first and second platesandsaid tubes so as to effect a sealed relationship between the ends ofsaid filter tubes and said plates, the tie rod passing through theaperture provided for it in the first plate and attaching to the secondplate and the tie rod and fastening means being adapted to allow for thetightening of said plates against said tubes refractory sealant materialis a fibrous alumina-silica.

when the cartridge is heated to operating temperasheet material.

tures. 4. The cartridge of claim 3 wherein said platesptie rod andfastening means are of cast iron.

7. The cartridge of claim 3 wherein said refractory particles arealumina.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 I 7 I765 Dated ly 24 r 1973 inventor) Thomas A. Nowak It, is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column 2, Line 7, "us" should be ---use- Column 3, Line 49, "simple"should be single Column 7, Line 33, "quanity" should be quality- Column8, Line 26, "mans" should be means Signed and 'sealed this 25th day ofDecember 1973.

(SEAL) Attest:

EDWARD M. FIETGiER,JR. RENE D. TEGTMEYER Attesting- Officer ActingCommissioner of Patents USCOMiMPDC 60876-P69 fl' 0.5. GDVERNME NTPRINTING OFFICE: l9, O-Jil-JJI.

05M Po-1oso (10 69)

2. An assembly as in claim 1, having also means to grasp and lift saidcartridge.
 3. A demountable cartridge for filtering molten aluminumcomprising in combination: a. at least one filter tube having aninterior passageway and formed of a rigid porous material havinginner-communicating pores, said material consisting essentially of afired mixture of refractory particles resistant to attack by moltenaluminum, said particles having an average maximum diameter of fromabout 0.165 to about 2.8 mm, and a prefused vitreous bonding materialconsisting essentially of, by weight, from 15% to 80% boron oxide, from5% to 50% calcium oxide and from 2% to 60% aluminum oxide and not morethan 10% silica said bonding material being uniformly dispersedthroughout said mixture, surrounding said particles and adhering themtogether, b. a first metal plate resistant to attack by molten aluminumadjacent one end of said filtering tube, said plate having at least oneaperture adapted to receive a tie rod and an aperture for each filtertube adapted to be in fluid communication with the interior passagewayof said filter tube and having a peripheral recess in the under face ofthe metal plate, c. a second metal plate resistant to attack by moltenaluminum adjacent the opposite end of said filter tube, said platehaving in its upper face a recess for each filter tube and means forattachment thereto of said tie rod, d. a compressible refractory sealantmaterial resistant to attack by molten aluminum disposed between theends of each filter tube and said plates, whereby the plates and tubesare maintained in sealed relationship upon expansion thereof, and e. atleast one tie rod and fastening means formed of a metal resistant toattack by molten aluminum joining said first and second plates and saidtubes so as to effect a sealed relationship between the ends of saidfilter tubes and said plates, the tie rod passing through the apertureprovided for it in the first plate and attaching to the second plate andthe tie rod and fastening means being adapted to allow for thetightening of said plates against said tubes when the cartridge isheated to operating temperatures.
 4. The cartridge of claim 3 whereinsaid plates, tie rod and fastening means are of cast iron.
 5. Thecartridge of claim 3 having a means to grasp and lift said cartridge. 6.The cartridge of claim 3 wherein said compressible refractory sealantmaterial is a fibrous alumina-silica sheet material.
 7. The cartridge ofclaim 3 wherein said refractory particles are alumina.